Direct3D 10: Vertex shaders texture fetch

Vertex Texture Fetch tests measure the speed of many vertex texture fetches. These tests are essentially similar, and the correlation of their results in Earth and Waves tests must also be similar. Both tests use displacement mapping based on texture fetches. The only major difference is that the Waves test uses conditional branches, while the Earth test does not.

Let's analyze the first test (Earth) in Effect detail Low mode:

Judging by our previous reviews, this test is heavily affected by memory bandwidth - the easier the mode, the stronger its effect on performance. It's apparent in relative results of GeForce 9800 GTX and GeForce 8800 Ultra - the latter is victorious in the Low mode (owing to its much higher memory bandwidth), the average results are similar. And they are practically identical in the most complex mode.

The dual-GPU 9800 GX2 is not much faster, although the HD 3870 X2 demonstrates a two-fold performance gain versus the HD 3870. Perhaps, it's the problem with drivers, that is with the AFR mode. Nevertheless, even GeForce 8800 Ultra performs better than HD 3870 X2. And GeForce GTX 280 is the formal leader. Let's have a look at results of this test with more texture lookups:

The situation hasn't changed much. GTX 280 is still victorious in the Low mode, but the 9800 GX2 comes forward in the High mode. However, GeForce GTX 280 is still faster than both cards from AMD and a tad faster than single-GPU GeForces 8 and 9. Just like in the previous case, results of the graphics cards grow closer, as the task gets more complex.

Let's have a look at results of the second vertex texture fetch test. The Waves test executes fewer texture lookups, but it uses conditional branches. The number of bilinear texture lookups in this case reaches 14 (Effect detail Low) or 24 (Effect detail High) per each vertex. Geometry complexity changes just like in the previous test.

The Waves test favors AMD products. The single-GPU card from the RADEON HD 3800 family looks good, it outperforms the G92-based card in the Low mode, being slightly slower in the High mode. We can see that performance in this test depends not on TMUs, but on memory bandwidth and fill rate, because even the dual-G92 card performs on a par with GeForce 8800 Ultra of the last but one generation. GeForce GTX 280 is the fastest solution in the Low mode, but in the other two modes it's outperformed by the dual-GPU RADEON. Let's analyze the second modification of the test:

There are not many changes here. As the test grows more complex, RADEON HD 3800 results become a tad better relative to NVIDIA performance. The latter cards loose more performance here. The other conclusions also hold true - performance is mostly limited by memory bandwidth, especially in the Low mode. TMUs and the second core start to play an important role in the High mode, so GeForce 9800 GX2 catches up with GTX 280 and outperforms HD 3870 X2. AMD cards have noticeably improved their positions in the VTF tests. We previously noted that NVIDIA cards coped better with vertex texture fetches, but now the situation has changed.

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